Military ground mobility vehicles often operate in areas of high heat with no environmental conditioning systems for cooling the individual soldier or critical vehicle electronic systems. It is well documented that working in extremely hot environments leads to reduced physical and cognitive performance. Typical vehicle climate control systems are large refrigerant-based systems that are not man portable.
Portable cooling methods and/or systems would be beneficial not only for military applications but also, for example, in sports (e.g. cooling athletes during training and competition), industrial and medical applications.
Currently, there are a number of potential cooling methods and/or systems as well as application methods but each have there own disadvantages. The following is a list of some of these examples:                refrigeration cycle based cooling        vortex cooling        thermoelectric based cooling        liquid cooled vests        passive (phase change) vests        air cooled vests        
With respect to refrigeration cycle based cooling, Rankine cycle refrigeration is an efficient method of heating and cooling. At least one variation has been deployed in combat operations. The system however does not support dismounted operations and requires integration into the vehicle's air-conditioning system or an air-conditioning system must be retrofitted to the vehicle if it is not so equipped.
With respect to vortex cooling, the Ranque-Hilsch vortex tube is a simple device that has no moving parts. Vortex tubes are popular in the industry for spot cooling of machinery, processes and electronic equipment. A number of manufacturers have incorporated them into cooling garments as well as respiration systems and although simple and very effective, they do require high volumes of compressed air in order to operate. A typical vortex tube based personnel cooling system may consume from 10 to 25 SCFM of air at 100 psi for example. This restricts mobility to a fixed compressed air source or requires compressed air to be carried which is not practical in most cases due to increased mass and short operational duration.
With respect to thermoelectric devices (TEDs), TEDs have been used extensively in cooling and heating applications since their commercial inception in the 1950's. Typical applications include compact refrigerators/warmers, water coolers, electronic cooling and temperature references as well as biomedical systems. Unfortunately the current generation of TEDs is relatively inefficient when compared to Rankin cycle refrigeration systems on a power/heat in/heat out basis or coefficient of performance (COP).
With respect to liquid cooled vests, these vests have found extensive use in a variety of personnel cooling applications over the years. The cooling sources are typically refrigeration systems or thermal storage (ice water) based but there have been some examples utilizing TED s. Refrigeration and thermal based systems can limit their mobility in mass and/or space sensitive applications. Traditional TED based configurations have been power intensive primarily due to low efficiency and high interface resistance and losses. Because this is a form of thermal contact cooling, the device must operate with a cooling temperature below about 37° C. (98° F.). This higher ΔT in relationship to ambient temperature can increase power demands when using this approach.
With respect to passive cooled vests, these vests have found limited use for personnel cooling in certain military environments. The vest contains packages of eutectic salts or parafinitic hydrocarbons which absorb heat and cool by phase change and thermal storage. They are typically designed to operate at about 21° C. (65° F.). This temperature range is advantageous as it provides good recharging characteristics using only ice water or refrigeration while minimizing vasoconstriction that would further increase cooling resistance as excessively cold temperatures are not directly applied to the subject. The user, however, must have access to a cold source as previously described in order to thermally recharge the vest. This would greatly limit its effectiveness as a portable garment.
With respect to air-cooled vests, certain designs of air cooled vests work primarily by removing heat trapped under the user's outerwear. This is effective with heavy or insulated outerwear or in cases where solar loads may be high, providing that the ambient air temperature is below or not significantly above body temperature. The user of the air-cooled vest must drink water constantly to keep from becoming dehydrated. Some commercial examples of air-cooled vests utilize vortex cooling tubes discussed above and other examples of air cooled vests employ controlled release and expansion of compressed carbon dioxide to provide cooling. This approach is interesting as CO2 also acts as a topical vasodilator reducing the body's resistance to cooling. Unfortunately, high concentrations of CO2 can form carbonic acid when contacting the skin or mucus membranes. Hypoxia and hypercapnia are also potential hazards when operating this type of system in a poorly ventilated or enclosed area. Notably, hypercapnia has been shown to increase the core cooling rate in humans.
There is a need for temperature controlling methods and/or systems that mitigate and obviate at least one or more of the disadvantages of the prior art systems.